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Xlib only uses XCB essentially as a transport layer. It still has the same bad implementation on top of that.
I think you need to check your driver configuration or talk to some X.org devs because unless you have a really crappy gfx card (and it sounds like you don't), you shouldn't be seeing those issues. I have a T500 with a Radeon 3650 in it and it is quite snappy and I don't see artifacts or tearing. Compositing is also quite usable, which will significantly reduce flickering (just like in Windows Vista/7).